To determine the congruence transformation from triangle \( \triangle ABC \) to triangle \( \triangle DEF \), we need to identify the transformations that result in the correct positional shifts and orientations of the triangles.
Let's analyze the possible transformations given:
- Reflecting across the y-axis changes the x-coordinates of the points (from \( (x, y) \) to \( (-x, y) \)).
- Shifting up or down changes the y-coordinates (adding or subtracting from the y-coordinate).
- Rotating \( 180° \) (clockwise or counterclockwise) changes the coordinates as well (from \( (x, y) \) to \( (-x, -y) \)).
To decide the correct transformation, consider the sequence of transformations that involve shifting and reflecting or rotating.
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If triangle \( ABC \) is shifted two units to the right and two units up, its coordinates change as follows:
- Original: \( (x, y) \)
- After shifting: \( (x + 2, y + 2) \)
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Reflecting it across the y-axis changes the x-coordinates:
- Final coordinates after shifting and reflecting: \( (-x + 2, y + 2) \)
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Compare these results to triangle \( DEF \) to see which sequence matches.
After computing and analyzing, the transformation sequence that accurately transitions from \( \triangle ABC \) to \( \triangle DEF \) is:
- Shift 2 units to the right and 2 units up, then reflect across the y-axis.
Thus, the correct response is: △ABC was shifted 2 units to the right and 2 units up, then reflected across the y-axis.